Radio Frequency Identification (RFID) is a technology frequently used to identify a target object. An RFID system typically includes an information carrying module known as a tag. A tag may include a microchip having an antenna and may be packaged such that it can be applied to the target object. The tag receives and transmits signals to and from a reader, most often packaged in the form of a transceiver. The tag may contain a unique serial number as well as other information, such as a customer account number. Tags may be implemented in many forms. For example, a tag may have a barcode label printed thereon, may be mounted inside a carton or may be embedded within the target object.
RFID tags may be implemented as active, passive or semi-passive devices. RFID tags function in response to coded RF signals received from a base station transceiver. An active tag generally includes its own energy supply, such as a battery, that may serve as a partial or complete power source for the tag's circuitry and antenna. Batteries may be replaceable or sealed units. A passive tag is generally powered by the RFID reader itself and thus generally does not contain a battery. It typically communicates by reflecting an incident RF carrier back to the reader. As radio waves from the reader are encountered by a passive RFID tag, a voltage is induced from the antenna. The tag may draw power from the induced voltage to energize its circuits. The tag then transmits the encoded information stored in the tag's memory by backscattering the carrier of the reader. A semi-passive RFID tag typically uses a battery to operate its internal circuitry, but also relies on backscattering communication.
Reading is the process of retrieving data stored on an RFID tag by propagating radio waves to the tag and converting the waves propagating from the tag to the reader into data. Information is transferred as the reflected signal is modulated by the tag according to a particular programmed information protocol. Protocols for RFID tags may be categorized in terms of tag to reader over the air interfaces. Three common interface classes are Class-0 (read-only), Class-1 (read/write), and UHF Generation-2 (read/write), for example. UHF Generation-2 provides some improvement upon existing Class-0 and Class-1 standards for worldwide operation and improved performance, for example. ISO18000 standard series RFID tags cover both active and passive RFID technologies.
FIG. 1 is a schematic diagram of one known prior art RFID tag 10 which includes an antenna 12 which is coupled by an impedance matching circuit 14 to an RF port 18 of RF circuit 20. In this example, the impedance matching circuit 14 includes a balun type transformer to match the impedance of the RF circuit 20. The impedance matching circuit 14 may include additional inductive or capacitive components, depending upon the particular application.
The RF circuit 20 typically includes a transceiver which demodulates the incoming RF signal and decodes it in accordance with one or more protocols. The RF circuit 20 often can store data decoded from the incoming RF signals and can retrieve data to be encoded and modulated into outgoing RF signals which are transmitted by the antenna 12. The RF circuit 20 can also scavenge power from the incoming RF signals and store that power to power the circuitry of the RFID tag 10.
FIG. 2 is a top view of a prior art RFID tag 10 which has been integrated on a single substrate 30. The antenna 12 is formed as a metallization deposited on the surface of the substrate 30. The RF circuit 20 and impedance matching circuit may be integrated on the same substrate 30 or on one or more additional integrated circuit substrates. The integrated circuit or circuits of the tag 10 may be encapsulated in one or more packages.
An RFID tag such as the RFID tag 10 may be embedded in a product and may be used for inventory control of that product, for example. Also, an RFID tag may be embedded in a product having additional circuitry which interacts with the circuitry of the RFID tag. For example, an RFID tag may be embedded in a sensor such that the output of the sensor may be read by interrogating the RFID tag with a wireless signal. There are numerous other applications for RFID tags.